This invention relates to apparatus used in the production of business forms and, more particularly, to uniquely designed sealing wheels utilized to activate pressure sensitive adhesives typically used to secure two or more sheets or plies of a multi-layer business form. The invention also relates to a method of utilizing such sealing wheels in the production of forms or the like.
In the production of business forms, it is often the case that a multi-layer form (including one or more removable inserts) requires perimeter sealing, i.e., sealing along as few as one or as many as four marginal edge portions of the form, but not in the central area of the form, within the marginal edge portions. This is often accomplished through the use of pressure sensitive adhesive selectively applied along such marginal edge portions. In a system developed by the assignee of this invention, multiple two wheel or roller pairs are employed in close sequence to effect the activation of the pressure sensitive adhesive at each of the sealing positions of the sealing apparatus. In order to produce a secure seal, the wheel pairs require loading on the order of 200 pounds per lineal inch of sealing width. This load must be managed with adequate steering of the plies of the form to be sealed in order to maintain tolerable register between the plies so as to prevent one ply from "creeping" sideways. In addition, the loading of the wheel or roller pairs must be carried out in such a way as to effect perimeter sealing without localized stretch of the paper of one or more of the plies.
Further problems which exacerbate the out-of-register condition are the difficulties encountered in attempting to achieve perfectly parallel tracking of the pressure wheels, and equally significant difficulties in attempting to assure that the multiple layers of the form are fed in perfect synchronism.
The effect of inadequate pressure, of course, will be that an inadequate seal is produced. At the same time, unequal web feeding could create a void or pucker in one or more corners of the form after exiting the sealer apparatus. Moreover, excessive pressure could produce paper stretch in the seal line area which would be asthetically unacceptable, and could cause stacking and handling problems in successive equipment, such as mail sorting machinery.
The present invention seeks to alleviate or eliminate these problems by utilizing a modified pressure wheel in each of the multiple two roller pairs. The modified pressure wheel in one exemplary embodiment of the invention is formed with a plurality of teeth similar to a helical gear about its peripheral edge sealing surface in order to effect an interrupted seal line along the pressure sensitive adhesive strip on the form. The purpose of the plurality of teeth is to increase the actual sealing pressure on the adhesive strip while, at the same time, allowing each incrementally small feed error on one or both of the plies to "escape" between the teeth of the sealing couple as it is processed through the sealer system. This increase of sealing pressure is directly proportional to the inverse ratio of tooth length to tooth-to-tooth pitch spacing. Additionally, the purpose of the helical gear cut is to maintain a contact angle greater than one-to-one which will operate as smoothly as a plain (smooth) wheel as long as the lateral contact across the face of the wheel pair is tolerably even.
In a preferred embodiment, the lower wheel or roller in each of two successive roller pairs is formed in the manner of a helical gear with the helix angle of the teeth on the first of the wheels arranged so as to extend substantially perpendicularly relative to the helix angle of the teeth on the second of the successive gears. In this manner, a cross hatch pattern is impressed on the pressure sensitive adhesive strip to thereby activate the pressure sensitive adhesive in the cross hatched areas, while leaving spaces between the cross hatching unactivated.
It will also be appreciated that greater or lesser degrees of adhesion can be achieved by varying spacing between the helical gear teeth formed on the sealing wheels or rollers. In other words, decreasing the spacing between teeth will increase the degree of adhesion, while increasing the space between the teeth will decrease the degree of adhesion, resulting in an easy open type form.
In the production of business forms, it is well known that such forms can be produced in continuous web form or in individual cut form. In either case, where pressure sensitive adhesive strips have been applied along transversely spaced longitudinal marginal edge portions of the form and/or web, multiple two wheel pairs are employed with a first set in lateral alignment, and a second set also in lateral alignment, but located downstream of the first set. In other words, at a first station, two identical wheel pairs each comprising a smooth upper roller and a patterned lower roller will simultaneously effect partial activation of the pressure sensitive adhesive applied along both longitudinal marginal edge portions of the form. Downstream of this first station, two identical wheel pairs (identical to each other but with helix angles perpendicular to the helix angles of the wheels at the first station) will effect the final activation of the pressure sensitive adhesive along both longitudinal marginal edge portions in the cross hatch pattern described hereinabove. In the event longitudinally spaced, transverse pressure sensitive adhesive strips are applied to the form, a similar arrangement of sealer wheels may be employed to activate the adhesive, after the form has been turned ninety degrees with respect to its original direction of movement.
A system as described above but without the patterned rollers described herein, is disclosed in commonly assigned copending application Ser. No. 07/417,775 filed Oct. 6, 1989 now U.S. Pat. No. 5,397,427. It will be appreciated, however, that the pressure sealing wheels in accordance with this invention can be utilized in many other pressure sealing systems as well.
Thus, in its broader aspects, the present invention relates to apparatus for effecting activation of pressure sensitive adhesive applied to predetermined portions of a business form, the improvement comprising pressure imparting surface means for providing a selectively interrupted pattern of pressure in the predetermined portions of the form.
In another aspect, the invention provides apparatus for activating pressure sensitive adhesive on predetermined portions of a first sheet in order to fasten the first sheet to a second sheet comprising means for applying pressure along the adhesive to effect a rhythmically interrupted sequence of sealed spots between the first and second sheets.
In another aspect of the invention, there is provided apparatus for applying pressure to a business form to activate pressure sensitive adhesive applied along at least one strip portion of the form to seal one part of the form to another, comprising a frame; and a pressure applying device operatively connected to the frame; the pressure applying device comprising means for applying pressure along a first strip while simultaneously conveying business forms therethrough, including a first set of narrow width upper and lower sealing rollers forming a nip, the upper roller disposed above and in peripheral engagement with the lower roller along a common vertical center line, one of the upper and lower rollers having an interrupted pattern formed on a pressure applying surface thereof.
In still another aspect of the invention, there is provided, broadly, a method of handling business forms, each having at least one strip of pressure sensitive adhesive of a predetermined width for fixing one part of the business form to another part, comprising the step of (a) automatically, in a continuous, sequential manner, acting on successive business forms to apply a force thereto in an interrupted pattern along the strip sufficient to activate selected portions of the pressure sensitive adhesive to fix one part of the form to another, the force being applied only to the approximate area of the predetermined width of adhesive.
In a related aspect, the invention relates to a method of activating at least one pressure sensitive adhesive strip for securing a first paper ply to a second paper ply comprising the steps of a) providing at least a first set of sealing rollers comprising an upper roller and a lower roller, each of which have pressure applying peripheral surfaces substantially equal to a width dimension of the strip, the pressure applying peripheral surface of one of the rollers comprising a first raised pattern extending about the circumference of the one roller; and b) feeding the first and second plies through the first set of sealing rollers, to thereby activate only portions of the pressure sensitive adhesive strip corresponding to the first raised pattern.
In still another aspect, the invention relates to a method of activating pressure sensitive adhesive strips for securing two sheets together along selected strip portions thereof without causing undesirable paper stretching, comprising the steps of a) providing at least a first set of sealing wheels comprising an upper wheel and a lower wheel, each of which have pressure applying peripheral surfaces substantially equal to a width dimension of said strip, the pressure applying peripheral surface of one of the wheels comprising a raised pattern extending about the circumference of the one wheel; and b) feeding the first and second plies through the first set of sealing wheels, to thereby activate only portions of the pressure sensitive adhesive strip corresponding to the raised pattern.